When people ask, “What are the two types of OPC?” they are usually referring to the two primary OPC specifications used in industrial automation: OPC Classic and OPC UA (Unified Architecture). OPC Classic is the original, Microsoft Windows–based set of standards built on COM/DCOM technology. OPC UA is the modern, platform-independent evolution that improves security, scalability, and interoperability across devices, systems, and operating environments.
OPC Classic
OPC Classic was introduced in the mid-1990s by the OPC Foundation to standardize communication between industrial devices and Windows-based software applications. It includes specifications such as:
- OPC DA (Data Access) – Real-time data exchange
- OPC HDA (Historical Data Access) – Access to archived data
- OPC A&E (Alarms & Events) – Alarm and event notifications
OPC Classic relies heavily on Microsoft’s COM/DCOM technology. While it served the industry well for many years, it can be difficult to configure securely—especially across firewalls or wide-area networks. As industrial systems expanded beyond isolated Windows environments, these limitations became more noticeable.
OPC UA (Unified Architecture)
OPC UA was developed to address the shortcomings of OPC Classic. It is platform-independent, meaning it can run on Windows, Linux, embedded systems, and even in the cloud. Unlike Classic, OPC UA was built with security in mind from the ground up, including encryption, authentication, and certificate-based trust models.
Key advantages of OPC UA include:
- Cross-platform compatibility
- Built-in security
- Scalability from embedded devices to enterprise systems
- Support for complex data modeling
OPC UA also supports both client-server and publish/subscribe communication models, making it suitable for modern Industrial IoT (IIoT) architectures.
Why the Difference Matters
Understanding the two types of OPC is important for system integrators, automation engineers, and IT teams planning upgrades or new deployments. Many legacy systems still run on OPC Classic, but new projects overwhelmingly favor OPC UA for its flexibility and security. If you are designing a modern automation system, OPC UA is generally the strategic choice, while OPC Classic may still appear in brownfield environments that require integration with older equipment.